1. Field of the Invention
The present invention relates generally to a fluorescent lamp, and more particularly to a long life fluorescent lamp adapted to function with high frequency electronic ballasts already present in the marketplace.
2. Description of Related Art
T8 fluorescent lamps have become quite popular in North American markets, and have largely supplanted the previous generation T12 fluorescent lamps due to their inherent higher efficiency. A typical North American 4-foot T8 fluorescent lamp using the known three component rare earth phosphor blends operates on a high frequency electronic ballast and has a life of about 20,000 hours.
It is desirable to increase the life of T8 fluorescent lamps, preferably by at least 30% (i.e. to at least 26,000 hours). There currently exist no long-life lamps having a life of at least 26,000 hours. Furthermore, conventional and known methods for extending lamp life (i.e. use of heavier gases, such as krypton, in the fill gas; use of double cathodes; etc.) often reduce lumen output compared to standard lamps.
While longer lamp life translates into cost savings to the consumer, it is unlikely that consumers will be willing to sacrifice performance for service life. In addition to cost savings, longer life is also desirable to reduce the environmental impact associated with frequent disposal of mercury-containing burned-out fluorescent lamps.
Consequently, there is a need for a long life T8 fluorescent lamp having a life of at least 26,000 hours that produces similar light (lumen) output compared to standard T8 lamps. Preferably, such a long-life lamp functions with currently emplaced high-frequency electronic ballasts.
A long life mercury vapor discharge lamp is provided having a light-transmissive glass envelope that has an inner surface, means for providing a discharge, an ultraviolet reflecting barrier layer of alumina particles coated adjacent the inner surface of the glass envelope, a phosphor layer coated adjacent the barrier layer, and a discharge-sustaining fill gas of mercury vapor and argon sealed inside the envelope. The fill gas has a pressure of 2.9-5 torr at 25xc2x0 C., and the phosphor layer has a coating weight of 2-3.5 mg/cm2.